Hybrid power system for locomotive

ABSTRACT

A hybrid power system for a locomotive for reducing emissions. The hybrid power system may have at least one engine powered by natural gas, at least one engine powered by diesel fuel and/or a dual fuel mixture of diesel and natural gas, a drive system operatively coupled to the at least one natural gas powered engine and the at least one diesel and/or dual fuel powered engine for propelling the locomotive, and a system controller for independently controlling power output from the respective engines to the drive system based upon a power demand. The hybrid power system may utilize the natural gas powered engine(s) at low power demands, and then supplement this power with the diesel and/or dual fuel powered engine(s) at higher power demands.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 62/508,620 filed May 19, 2017, which is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to locomotives, and more particularly to a hybrid power system for a locomotive that utilizes both natural gas and diesel power.

BACKGROUND

Existing railroad locomotives are typically powered by diesel electric systems in which a diesel powered engine drives an electric generator to produce electric power, which energizes electric motors that propel drive wheels of the locomotive. The diesel powered engines, however, are notorious for their poor emissions ratings, particularly emissions of nitrogen oxides (NOx) which cause smog, ozone and other air pollutions, diesel particulate matter (PM) which are carcinogenic to humans, and greenhouse gases. As such, railroads are under increased pressure to reduce emissions and fuel consumption. One of several responses to these pressures has been the development of engines that consume only cleaner burning natural gas fuel. However, even though these natural gas powered engines may reduce emissions and fuel consumption in certain rail situations, such as yard switching, they are less effective for medium haul freight or commuter trains due to their low horsepower rating and the relatively low power density of the gaseous fuel. Another response to the pressures to reduce emissions has been the development of dual fuel engines that consume both diesel fuel and the cleaner burning natural gas fuel. However, while these dual fuel engines may provide greater horsepower than solely natural gas powered engines, and also may provide reduced emissions compared to diesel only powered engines, the dual fuel engines still consume diesel fuel regardless of the locomotive's power demand, and thus these dual fuel engines are not expected to meet more stringent emissions regulations.

SUMMARY

The present disclosure provides a hybrid power system for a locomotive that minimizes emissions by utilizing the benefits of a cleaner burning natural gas powered engine at lower power demands, and then supplements the natural gas powered engine with a diesel powered engine at higher power demands. Such a hybrid power system may enable the locomotive to reduce emissions over a wide range of available horsepower, which therefore enables cleaner operation over a wide range of distances, including long and short hauls.

According to one aspect of the present disclosure, a hybrid power system for a locomotive includes at least one engine powered by natural gas; at least one engine powered by diesel fuel and/or a dual fuel mixture of diesel and natural gas; a drive system operatively coupled to the at least one natural gas powered engine and the at least one diesel and/or dual fuel powered engine for propelling the locomotive; and a system controller operatively coupled to the at least one natural gas powered engine, the at least one diesel and/or dual fuel powered engine, and the drive system for controlling power output from the respective engines to the drive system.

According to an aspect of the present disclosure, the system controller may be configured to: i) determine a desired power level for propelling the locomotive; ii) command the at least one natural gas powered engine to supply power to the drive system up to a maximum power output of the at least one natural gas powered engine; and iii) when the desired power level exceeds the maximum power output of the at least one natural gas powered engine, command the at least one diesel and/or dual fuel powered engine to supply power to the drive system to supplement the power supplied by the natural gas powered engine.

According to another aspect of the present disclosure, a method of operating a locomotive with a hybrid power system includes: i) determining a desired power level for propelling the locomotive; ii) commanding at least one natural gas powered engine to supply power to a drive system up to a maximum power output of the at least one natural gas powered engine for propelling the locomotive; and iii) when the desired power level exceeds the maximum power output of the at least one natural gas powered engine, commanding at least one diesel and/or dual fuel powered engine to supply power to the drive system to supplement the power supplied by the natural gas powered engine.

The following description and the annexed drawings set forth certain illustrative embodiments according to the present disclosure. These embodiments are indicative, however, of but a few of the various ways in which the principles according to the present disclosure may be employed. Other objects, advantages and novel features according to aspects of the disclosure will become apparent from the following detailed description when considered in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The annexed drawings, which are not necessarily to scale, show various aspects according to the present disclosure.

FIG. 1 is a schematic block diagram of an exemplary locomotive having an exemplary hybrid power system according to an embodiment of the present disclosure.

FIG. 2 is a flow chart showing an exemplary method of operating the hybrid power system according to an embodiment of the present disclosure.

FIG. 3 is a schematic side view of an exemplary locomotive having an exemplary hybrid power system according to an embodiment of the present disclosure.

FIG. 4 is an enlarged perspective view of an exemplary modular unit shown in FIG. 3, the modular unit containing at least one natural gas powered engine and at least one storage tank for gaseous fuel according to an embodiment of the present disclosure.

FIG. 5A is a table illustrating an exemplary configuration of an exemplary hybrid power system according to an embodiment of the present disclosure. FIG. 5B is a continuation of the table in FIG. 5A.

FIG. 6A is a table illustrating another exemplary configuration of an exemplary hybrid power system according to another embodiment of the present disclosure. FIG. 6B is a continuation of the table in FIG. 6A.

FIG. 7A is a table illustrating another exemplary configuration of an exemplary hybrid power system according to another embodiment of the present disclosure. FIG. 7B is a continuation of the table in FIG. 7A.

DETAILED DESCRIPTION

Referring to FIG. 1, an exemplary locomotive 10 having an exemplary hybrid power system 12 is shown. Generally, the hybrid power system 12 has at least one engine powered by natural gas 14 (also referred to as a natural gas powered engine(s) 14), at least one engine powered by diesel fuel 16 (also referred to as a diesel powered engine(s) 16), and a drive system 18 operatively coupled to the natural gas powered engine(s) 14 and the diesel powered engine(s) 16 for propelling the locomotive 10. The hybrid power system 12 also includes at least one system controller 20 operatively coupled to the at least one natural gas powered engine 14, the at least one diesel powered engine 16, and the drive system 18 for independently controlling power output of the respective engines 14, 16 based upon the power demand for propelling the locomotive 10. Generally, the system controller 20 is configured to minimize the average emissions rate from the respective engines (e.g., 14, 16), including emissions such as nitrogen oxides (NOx), particulate matter (PM), and/or hydrocarbons (NC), as discussed in further detail below.

As shown in the illustrated embodiment, the hybrid power system 12 may include a plurality of natural gas powered engines 14 that are solely powered by natural gas fuel. In exemplary embodiments, the natural gas powered engines 14 may have a NOx emission rate of less than 1.0 g/bhp-hr, more particularly less than 0.5 g/bhp-hr, more particularly less than 0.1 g/bhp-hr, and more particularly about 0.02 g/bhp-hr (also referred to as “near-zero” emissions), or less. In exemplary embodiments, the natural gas powered engines 14 may have a power output of between 100-500 horsepower, more particularly about 320 to 400 horsepower. For example, one or more of the natural gas powered engines 14 may be a Cummins-Westport ISL G NZ (“near zero”) or Cummins-Westport ISX12 G NZ (“near zero”) engine (manufactured by Cummins-Westport of Vancouver, B.C., Canada) which is/are configured to be powered solely by natural gas fuel.

The hybrid power system 12 may further include one or more storage tanks 22 configured to store a natural gas supply for fueling the at least one natural gas powered engine 14. In exemplary embodiments, the storage tanks 22 are configured to store compressed natural gas (CNG) or also could be configured to store liquid natural gas (LNG). The one or more storage tanks 22 may be located onboard the locomotive 10, and/or the storage tanks 14 may be located in a separate tender car. In exemplary embodiments, the storage tanks 22 may be contained in a module along with the natural gas powered engine(s) 14, as shown in FIG. 3 and discussed in further detail below.

As shown, the hybrid power system 12 may include a plurality of diesel powered engines 16 that are powered solely by diesel fuel. In exemplary embodiments, the diesel powered engines 16 may have a NOx emission rate of less than 2.0 g/bhp-hr, more particularly less than 1.5 g/bhp-hr, more particularly about 1.3 g/bhp-hr or less, or more particularly about 0.8 g/bhp-hr, or less. In exemplary embodiments, the diesel powered engines 16 may have a power output of between 500-5,000 horsepower, more particularly between about 750-4,200 horsepower, such as about 950 horsepower, about 2,700 horsepower, about 4,200 horsepower, or greater. For example, one or more of the diesel powered engines may be a Cummins QSX15 Tier 4 (600 HP), a QSK23 Tier 4 (950 HP), a QSK60 Tier 4(2700 HP), or a QSK95 Tier 4 (4500 HP) diesel engine (manufactured by Cummins Inc. of Columbus, Ind., USA) that is/are configured to be powered by diesel fuel. As shown, the hybrid power system may further include one or more onboard storage tanks 24 configured to store a diesel fuel supply for fueling the diesel powered engines 16.

The hybrid power system 12 also may optionally include at least one dual fuel engine 26 powered by both natural gas and diesel fuel (also referred to as a dual fuel engine(s) 26. As shown, the dual fuel engine(s) 26 may receive natural gas fuel from the storage tanks 22, and also may receive diesel fuel from the storage tanks 24. As shown, the drive system 18 may be operatively coupled to the dual fuel engine(s) 26 for propelling the locomotive, and the system controller 20 may be operatively coupled to the dual fuel engine(s) 26 for controlling the power output of the dual fuel engine 26 based upon a determination of the desired power level to propel the locomotive 10. In this manner, it is understood that the dual fuel engine(s) 26 may be utilized in conjunction with the natural gas powered engine(s) 14 and the diesel powered engine(s) 16 to meet the power demand of the locomotive 10, while also reducing emissions. It also understood, however, that the dual fuel engine(s) 26 may substitute the diesel powered engine(s) 16 or the natural gas powered engine(s) 14 as desired to meet the power demands and emissions for a particular application, as understood by those having skill in the art.

The drive system 18 may be a mechanical-electric drive system 18 that includes one or more traction motors 28 drivingly coupled to wheels (shown in FIG. 3) for propelling the locomotive 10. For example, the at least one natural gas powered engine 14, the at least one diesel powered engine 16, and/or the at least one dual fuel engine 26 may be operatively coupled to a traction control system 30 to convert mechanical energy from the respective engines (14, 16, and/or 26) to electrical energy, thereby providing alternating current or direct current to the traction motors 28, which transmit power to wheels for propelling the locomotive 10. In this manner, the traction control system 30 may include one or more alternators and/or one or more electrical generators configured to convert the mechanical energy to electrical energy. Alternatively or additionally, the natural gas powered engine(s) 14, the diesel powered engine(s), and/or the dual fuel engine(s) 26 may be drivingly coupled to the wheels via a mechanical transmission, or may be operatively coupled to a hydraulic system for torque transmission and/or for enabling energy recuperation.

The hybrid power system 12 may further include at least one battery 32 for storing electrical energy. The battery 32 may be operatively coupled to the electrical generators of the traction control system 30 via the controller 20 for converting mechanical energy from the engines (14, 16, and/or 26) into electrical energy for charging the battery. In this manner, the battery 32 may be operatively coupled to the traction motors 28 for transmitting power to the wheels, and also may power the controller 20 or other electrical systems of the locomotive 10.

Also as shown in the illustrated embodiment, the hybrid power system 12 may further include a connection 34, such as an electrical bus (third rail, overhead power line, etc.), for being connected to an external power source, such as an external power line. As shown, the external power source 34 may be operatively coupled to the one or more traction motors 28 for transmitting power to the wheels, and also may be operatively coupled to the battery 32 for storing energy, or may provide power to the controller 20 or other electrical systems.

The at least one system controller 20 may include one or more sub-controllers or may include any apparatus, device, or machine for processing data and performing function(s) or an action(s), or to cause a function or action from another logic, method, or system. Generally, the system controller 20 is configured to individually control power distribution from the respective engines (14, 16, and/or 24), the battery 32, and/or the external power source 34 to the drive system 18, and more particularly to the traction motors 28, for transmitting power to the wheels to propel the locomotive 10. The controller 20 also may be configured to control the distribution of power from the engines (14, 16, and/or 24) and/or the external power source 34 to the battery 32 for storage of energy.

In exemplary embodiments, the controller 20 is configured to determine a desired power level for propelling the locomotive 10, and the controller 20 may independently control the power output of the respective engines (14, 16, and/or 24) based upon the power demand. For example, based upon the power demand, the controller 20 may command the natural gas powered engine(s) 14 to supply power to the drive system 18 up to a maximum power output of the natural gas powered engine(s). In this manner, for low power demands, the power supplied by the natural gas powered engine(s) 14 may be sufficient to propel the locomotive 10 as desired, and thus emissions may be minimized by utilizing only the low emissions natural gas powered engine(s). On the other hand, when the power demand exceeds the maximum power output of the natural gas powered engine(s) 14, the controller 20 may command the diesel powered engine(s) 16 (and/or the dual fuel engine(s) 26) to supply power to the drive system 18 to supplement the power supplied by the natural gas powered engine(s) 14. In this manner, for the higher power demands, the diesel powered engine(s) 16 (and/or dual fuel engine(s) 26) may be utilized only to the extent necessary to supplement power so as to meet the total power demand for propelling the locomotive 10 as desired. By minimizing the utilization of the diesel powered engine(s) 16 (and/or dual fuel engine(s) 26) in this way may advantageously minimize the average total emissions of the locomotive 10. In exemplary embodiments, the hybrid power system 12 may be configured to control the power output of the at least one natural gas powered engine 14 and the at least one diesel powered engine 16 (and/or the at least one dual fuel engine 26) for minimizing the combined average emissions rate, preferably below 0.2 g/bhp-hr NOx as a percentage of the duty cycle according to a predefined notch schedule, as discussed in further detail below.

Referring to FIG. 2, an exemplary method 100 of operating the hybrid power system 12 via the at least one controller 20 is shown. The method may begin at step 102. At step 104, the controller 20 determines the power demand (e.g., desired power level) to propel the locomotive 10. This determination may be via an operator input, for example, by selecting a predetermined power level. For example, a plurality of discrete graduated power levels that correspond with increased power demands may be selectable by the operator. Such a configuration is shown in the examples of FIGS. 5A-7B, which illustrate a notch schedule of the locomotive, as discussed in further detail below. Alternatively or additionally, the controller 20 may utilize an algorithm to determine the power demand from each of the engines that is needed to attain a desired parameter, such as torque or speed at the engine or wheels, for example. It is also understood that the controller 20 may utilize known or measured quantities for making such calculations, such as by utilizing suitable sensors, data in databases, or the like.

At step 106, the controller 20 determines whether more power is required to meet the power demand that was determined at step 104. If no additional power is required, then the system may maintain its current state, as shown at step 108. This may be the case if the locomotive is already moving, for example. On the other hand, if additional power is required, for example to accelerate the locomotive, then at step 110 the controller 20 may command the at least one natural gas powered engine 14 to supply power to the drive system 18 to propel the locomotive 10 (either in forward or reverse, as desired). This state of powering the locomotive only with the low emissions natural gas powered engine(s) 14 may be particularly advantageous for minimizing emissions during low power demand situations.

After powering the drive system 18 with the natural gas powered engine(s) 14 at step 110, the controller 20 may again determine whether additional power is required to meet the power demand, as shown at step 112. If no additional power is required, then the system may maintain its current state, as shown at step 108. If additional power is required, then the controller 20 may determine whether additional power is available from the natural gas powered engine(s) 14, as shown at step 114. If additional power is available from the natural gas powered engine(s) 14, then the process may loop back to step 110 to command the natural gas powered engine(s) 14 to supply additional power to the drive system 18 to further propel (e.g., accelerate) the locomotive 10. In exemplary embodiments where a plurality of natural gas powered engines 14 are utilized, then the system controller 20 may command a first one of the plurality of natural gas powered engines 14 to supply power to the drive system 18 up to a maximum power output of the first natural gas powered engine 14, and when the desired power level for propelling the locomotive exceeds the maximum power output of the first natural gas powered engine 14, the controller 20 may command one or more additional natural gas powered engines 14 to supply power to the drive system 18 for supplementing the power output of the first natural gas powered engine 14. It is understood that although the controller 20 may command the multiple natural gas powered engines 14 sequentially in this way, the controller 20 also may command the natural gas powered engines 14 simultaneously for attempting to meet the power demand.

At step 114, if the controller 20 determines that the natural gas powered engine(s) 14 are at the (cumulative) maximum power output and no additional power is available, and that additional power is needed to meet the desired power level (e.g., further acceleration is needed), then the method may proceed to step 116. As shown at step 116, the controller 20 may command the at least one diesel powered engine 16 to supply power to the drive system 18 to supplement the power supplied by the natural gas powered engine(s) 14 in order to further propel the locomotive 10. This state of powering the locomotive 10 with both the low emissions natural gas powered engine(s) 14 and supplementing the power as needed with the diesel powered engine(s) 16 may enable lower average emissions over a wide range of desired power levels. This may advantageously enable the average total emissions rate from the engines to be below a desired threshold level over a wide range of distances, including long and short hauls.

After powering the drive system 18 with the diesel powered engine(s) 16 at step 116, the controller 20 may again determine whether additional power is required to meet the power demand, as shown at step 118. If no additional power is required, then the system may maintain its current state, as shown at step 108. If additional power is required, then the controller 20 may determine whether additional power is available from the diesel powered engine(s) 16, as shown at step 120. If additional power is available from the diesel powered engine(s) 16, then the process may loop back to step 116 to command the diesel powered engine(s) 16 to supply additional power to the drive system 18 to further propel the locomotive 10. In exemplary embodiments where a plurality of diesel powered engines 16 are utilized, then the system controller 20 may command a first one of the plurality of diesel powered engines 16 to supply power to the drive system 18 up to a maximum power output of the first diesel powered engine 16, and when the desired power level for propelling the locomotive exceeds the maximum power output of the first diesel powered engine 16, the controller 20 may command one or more additional diesel powered engines 16 to supply power to the drive system 18 for supplementing the power output of the first diesel powered engine 16. It is understood that although the controller 20 may command the multiple diesel powered engines 16 sequentially in this way, the controller 20 also may command the diesel powered engines 16 simultaneously for attempting to meet the power demand. At step 120, if no additional power is available from the engines (e.g., both the natural gas powered engine(s) 14 and the diesel powered engine(s) 18), then the hybrid power system may maintain its current state, as shown at step 108.

Although control of the hybrid power system 12 has been shown and described with respect to the exemplary method 100, it is understood that in other embodiments the hybrid power system 12 may add or eliminate one or more steps of the method 100. For example, in some embodiments, one or more of the decision steps (e.g., 106, 112, 114, 118 and/or 120) may be eliminated such that the controller 20 controls the hybrid power system 12 via predetermined commands according to predefined information that may be stored and accessed by the controller. For example, based upon an operator selecting a predefined power level (e.g., notch selection, as shown in FIGS. 5A-7B, for example)(via step 104, for example), the controller 20 may proceed to supply power via the natural gas powered engine (step 110), or the natural gas powered engine and the diesel powered engine (step 116), according to predefined engine parameters (e.g., engine speed (rpm), torque, horsepower, etc.). In this manner, the controller 20 may retrieve information from a database or look-up table, such that at each predefined power level (e.g., notch selection) there is a predefined command of which engine(s) to utilize, and how much horsepower should be delivered from each of those engine(s).

It is also understood that although the method 100 is shown with reference to the controller's operation of the natural gas powered engine(s) 14 and the diesel powered engine(s), that power from additional sources may be introduced into the method 100, as would be understood by those having skill in the art. For example, power from the battery 32 and/or external power source 34, which have essentially zero emissions, may be utilized as a source of power to propel the locomotive. The battery 32 and/or the external power source 34 may be utilized prior to utilizing the natural gas powered engine(s) 14, or may be utilized simultaneously with the natural gas powered engine(s) 14, or thereafter while utilizing the diesel powered engine(s) 16. In addition, in exemplary embodiments where one or more dual fuel engines 26 are provided (which may have emission rates between that of the natural gas engine 14 and the diesel engine 26), then these dual fuel engines 26 may be incorporated into the method 100 after utilizing the natural gas powered engine(s) 14, but before utilizing the diesel powered engine(s) 16, so as to supplement the cleaner burning natural gas power prior to bringing the diesel powered engine(s) 16 online. Alternatively, the dual fuel engine(s) 26 may be utilized in conjunction with the diesel engine(s) 16, or may substitute the steps associated with the diesel engine(s) 16 altogether in the method 100.

Referring to FIG. 3, a schematic side view of an exemplary unitary locomotive 210 having a hybrid power system 212 is shown. The locomotive 210 is substantially the same as the above-referenced locomotive 10, and consequently the same reference numerals but indexed by 200 are used to denote structures corresponding to the same or similar structures. As such, the foregoing description of the locomotive 10 is equally applicable to the locomotive 210.

As shown in the illustrated embodiment, the locomotive 210 includes one or more trucks 240 that are provided for riding on rails of a track. Each truck 240 may include an assembly of axles, wheels 242, traction motors 228, gearing, suspension, and brakes, which may be provided in a manner well-known in the art. The locomotive 210 also includes an undercarriage or deck 244, which is configured to ride on the trucks 240, and is also configured to support the natural gas powered engine(s) 214, the diesel powered engine(s) 216, and/or the dual fuel engine(s) (not shown). In addition, the deck 244 may support the natural gas storage tanks 222 and/or the diesel tanks 224, which may be mountable to the underside of the deck 244 between one or more trucks 240 as shown. In exemplary embodiments, the natural gas powered engine(s) 214 includes at least one of the natural gas powered engine(s) 14 discussed above, such as a natural gas (NG) near-zero (NZ) engine, for example a 320-horsepower Cummins Westport ISL G NZ engine manufactured by Cummins Westport of Vancouver, B.C., Canada. In exemplary embodiments, the diesel powered engine(s) 216 includes at least one of the diesel powered engine(s) 16 discussed above, such as at least one Tier-4 diesel engine having a horsepower in the range of 600-HP to 4200-HP, for example one or more of a 600-horsepower Cummins QSX15 engine and/or a 4200-horsepower Cummins QSK95 engine, both manufactured by Cummins Inc. of Columbus, Ind., USA. In exemplary embodiments, the natural gas powered engine(s) 214 and the natural gas storage tanks 222 may be part of a modular unit 250, as shown in FIG. 4, for example.

Referring to FIG. 4, the modular unit 250 containing the at least one natural gas powered engine 214 is shown in further detail. As shown, the modular unit 250 may include an enclosure 252, such as a reinforced cage, that may support the natural gas powered engine(s) 214. In exemplary embodiments, two natural gas powered engines 214 may be provided in the module 250. In addition, the modular unit 250 may have a space (e.g., below the engines 214) for storing one or more gas tanks 222, for example two, four, six or more tanks, which are configured to store the natural gas fuel (e.g., CNG or LNG fuel). The modular unit 250 may be a standalone unit, and may be utilized to easily retrofit or install a natural gas powered engine 214 on the locomotive 210, thereby facilitating the ability to use the hybrid power system 212.

Turning to FIGS. 5A-7B, various exemplary configurations of hybrid power systems are shown. In these exemplary embodiments, the respective hybrid power systems are configured to control power output from the respective natural gas powered engine(s) and/or the diesel powered engine(s) according to a predetermined notch schedule (column A), where each notch corresponds to a desired power level (column C). Generally, locomotive emissions are measured over two steady-state test cycles which represent two different types of service including: (a) switch locomotives (FIGS. 5A/5B and 6A/6B) and (b) line haul locomotives (FIG. 7A/7B). The duty cycles include different weighting factors for each of the eight throttle notch modes, which are used to operate locomotive engines at different power levels, as well as for idle and dynamic brake modes. As shown in FIGS. 5A/5B and 6A/6B, the switcher locomotive operation involves more time in idle and low power notches, whereas the line-haul locomotive operation (FIG. 7A/7B) is characterized by a higher percentage of time in the high power notches, such as notch 8. In exemplary embodiments, the hybrid power system is configured to control the power output of the natural gas powered engine(s) and the diesel powered engine(s) (and/or the dual fuel engine(s)) for minimizing the combined average emissions rate, preferably below 0.2 g/bhp-hr NOx as a percentage of the duty cycle according to a predefined notch schedule.

Referring particularly to FIG. 5A/5B, an exemplary hybrid power system for a 1,270 horsepower switcher locomotive is shown. The switcher locomotive includes one natural gas powered engine, such as a Cummins ISL G NZ engine having a maximum power output of about 320 horsepower and an emissions rate of about 0.02 g/bhp-hr NOx. The switcher locomotive also includes one diesel powered engine, such as a Cummins QSK23 engine having a maximum power output of about 950 horsepower and an emissions rate of about 1.3 g/bhp-hr NOx. As shown in the illustrated embodiment, at low power demands, such as at idle and notches 1-3 (e.g., 13-298 horsepower), only the low emissions natural gas powered engine is utilized to propel the locomotive. However, at notch 4 (column A), the power demand (e.g., desired power level) is at about 445 horsepower (column C), which exceeds the maximum power output of the natural gas powered engine (e.g., 320 horsepower). As such, the diesel powered engine is commanded to supplement the natural gas power up to the desired power level, which at notch 4 is an additional 125 horsepower provided by the diesel powered engine (as shown in column F). As shown, the total NOx of the weighted usage of the natural gas engine and diesel engine is about 0.38 g/bhp-hr (column O). As the notches continue to increase (e.g., from notch 4 up to notch 8), the diesel powered engine continues to supplement additional power to meet the corresponding power demand, and the percentage of horsepower provided by each engine shifts toward more diesel power usage (as shown in columns H and J). Advantageously, such a hybrid power system configuration is shown to produce only 0.086 NOx as an average percentage of the duty cycle according to the notch schedule (column P, last row), which is below a threshold of 0.2 g/bhp-hr NOx.

Referring to FIG. 6A/6B, an exemplary hybrid power system for a 1,410 horsepower switcher locomotive is shown. The switcher locomotive includes two natural gas powered engines, such as Cummins ISL G NZ engines, each having a maximum power output of about 320 horsepower and an emissions rate of about 0.02 g/bhp-hr NOx. The switcher locomotive also includes one diesel powered engine, such as a Cummins QSK23 having a maximum power output of 950 horsepower and an emissions rate of about 1.3 g/bhp-hr NOx. As shown in the illustrated embodiment, at low power demands, such as at idle and notches 1 and 2 (e.g., 14-162 horsepower), only one of the low emissions natural gas powered engines is utilized to propel the locomotive. At notches 3-4, the power demand exceeds the maximum power output of the one natural gas engine (e.g., 320 horsepower), and the other natural gas powered engine is commanded to supplement the power of the first natural gas powered engine (as shown in column E). At notch 5, the power demand is at about 684 horsepower, which exceeds the cumulative maximum power output of both natural gas powered engines (e.g., 640 horsepower). As such, the diesel powered engine is commanded to supplement the natural gas power up to the desired power level, which at notch 5 is about an additional 45-50 horsepower provided by the diesel powered engine (as shown in column F). As the notches continue to increase (e.g., from notch 5 up to notch 8), the diesel powered engine continues to supplement additional power to meet the corresponding power demand, and the percentage of horsepower provided by the engines shifts toward more diesel power usage (as shown in columns H, I, and J). Advantageously, such a hybrid power system configuration is shown to produce only 0.038 NOx as an average percentage of the duty cycle according to the notch schedule (column P, last row), which is below a threshold of 0.2 g/bhp-hr NOx.

Referring to FIG. 7A/7B, an exemplary hybrid power system for a 3,340 horsepower line haul locomotive is shown. The line haul locomotive includes two natural gas powered engines, such as Cummins ISL G NZ engines, each having a maximum power output of about 320 horsepower and an emissions rate of about 0.02 g/bhp-hr NOx. The switcher locomotive also includes one diesel powered engine, such as a Cummins QSK60 having a maximum power output of about 2,800 horsepower and an emissions rate of about 0.8 g/bhp-hr NOx. As shown in the illustrated embodiment, at low power demands, such as at idle and notch 1 (e.g., 33-150 horsepower), only one of the low emissions natural gas powered engines is utilized to propel the locomotive. At notch 2, the power demand (e.g., 384 horsepower) exceeds the maximum power output of the one natural gas engine (e.g., 320 horsepower), and the other natural gas powered engine is commanded to supplement the power of the first natural gas powered engine (as shown in column E). At notch 3, the power demand is at about 785 horsepower, which exceeds the cumulative maximum power output of both natural gas powered engines (e.g., 640 horsepower). As such, the diesel powered engine is commanded to supplement the natural gas power up to the desired power level, which at notch 3 is about an additional 145 horsepower provided by the diesel powered engine (as shown in column F). As the notches continue to increase (e.g., from notch 3 up to notch 8), the diesel powered engine continues to supplement additional power to meet the corresponding power demand, and the percentage of horsepower provided by the engines shifts toward more diesel power usage (as shown in columns H, I, and J). Advantageously, such a hybrid power system configuration is shown to produce only 0.20 NOx as an average percentage of the duty cycle according to the notch schedule (column P, last row), which is about at a threshold of 0.2 g/bhp-hr NOx.

A hybrid power system for a locomotive for reducing emissions has been described herein. The hybrid power system may have at least one engine powered by natural gas, at least one engine powered by diesel fuel and/or a dual fuel mixture of diesel and natural gas, a drive system operatively coupled to the at least one natural gas powered engine and the at least one diesel and/or dual fuel powered engine for propelling the locomotive, and a system controller for independently controlling power output from the respective engines to the drive system based upon a power demand. The hybrid power system may utilize the natural gas powered engine(s) at low power demands, and then supplement this power with the diesel and/or dual fuel powered engine(s) at higher power demands.

According to an aspect of the present disclosure, a hybrid power system for a locomotive includes: at least one engine powered by natural gas; at least one engine powered by diesel fuel and/or a dual fuel mixture of diesel and natural gas; a drive system operatively coupled to the at least one natural gas powered engine and the at least one diesel and/or dual fuel powered engine for propelling the locomotive; and a system controller operatively coupled to the at least one natural gas powered engine, the at least one diesel and/or dual fuel powered engine, and the drive system; wherein the system controller is configured to: i) determine a desired power level for propelling the locomotive; ii) command the at least one natural gas powered engine to supply power to the drive system up to a maximum power output of the at least one natural gas powered engine; and iii) when the desired power level exceeds the maximum power output of the at least one natural gas powered engine, command the at least one diesel and/or dual fuel powered engine to supply power to the drive system to supplement the power supplied by the natural gas powered engine.

Embodiments according to the present disclosure may include one or more of the following additional features, alone or in any combination.

The at least one natural gas powered engine may include a plurality of natural gas powered engines; and the system controller may be configured to: (i) command one or more of the plurality of natural gas powered engines to supply power to the drive system up to a maximum cumulative power output of the one or more natural gas powered engines; and (ii) when the desired power level for propelling the locomotive exceeds the maximum cumulative power output of the one or more natural gas powered engines, command one or more additional natural gas powered engines of the plurality of natural gas powered engines to supply power to the drive system for supplementing the cumulative power output of the first-mentioned one or more natural gas powered engines.

The at least one diesel and/or dual fuel powered engine may include a plurality of diesel and/or dual fuel powered engines; and the system controller may be configured to: (i) command one or more of the plurality of diesel and/or dual fuel powered engines to supply power to the drive system up to a maximum cumulative power output of the one or more diesel and/or dual fuel engines; and (ii) when the desired power level for propelling the locomotive exceeds the maximum cumulative power output of the one or more diesel and/or dual fuel powered engines, command one or more additional diesel and/or dual fuel powered engines of the plurality of diesel and/or dual fuel powered engines to supply power to the drive system for supplementing the cumulative power output of the first-mentioned one or more diesel and/or dual fuel powered engines.

The desired power level may include a plurality of discrete graduated power levels that are selectable, such as by an operator, for example, the discrete graduate power levels corresponding to a notch schedule.

The at least one natural gas powered engine and the at least one diesel and/or dual fuel powered engine may each have an emissions rate (e.g., g/bhp-hr) of one or more emissions including nitrogen oxides (NOx), particulate matter (PM), and/or hydrocarbons (NC); and the controller may be configured to control the power output of the at least one natural gas powered engine and the at least one diesel and/or dual fuel powered engine for minimizing the combined emissions rate, preferably below 0.2 g/bhp-hr NOx as an average percentage of the duty cycle.

The controller may be configured to control the power output of the at least one natural gas powered engine and the at least one diesel and/or dual fuel powered engine according to the principles of the example shown in FIG. 5A/5B, including corresponding ratios of horsepower, percentage horsepower, and NOx emission rates for achieving a desired NOx level, such as below 0.2 g/bhp-hr NOx.

The controller may be configured to control the power output of the at least one natural gas powered engine and the at least one diesel and/or dual fuel powered engine according to the principles of the example shown in FIG. 6A/6B, including corresponding ratios of horsepower, percentage horsepower, and NOx emission rates for achieving a desired NOx level, such as below 0.2 g/bhp-hr NOx.

The controller may be configured to control the power output of the at least one natural gas powered engine and the at least one diesel and/or dual fuel powered engine according to the principles of the example shown in FIG. 7A/7B, including corresponding ratios of horsepower, percentage horsepower, and NOx emission rates for achieving a desired NOx level, such as below 0.2 g/bhp-hr NOx.

The at least one natural gas powered engine may include a plurality of natural gas powered engines.

The at least one natural gas powered engine may have a NOx emission rate of less than 1.0 g/bhp-hr, more particularly less than 0.5 g/bhp-hr, more particularly less than 0.1 g/bhp-hr, and more particularly about 0.02 g/bhp-hr.

The at least one natural gas powered engine may have a power output of between 100-500 horsepower, more particularly about 320 to 400 horsepower.

The at least one natural gas powered engine may be powered only with natural gas.

The hybrid power system may further comprise one or more storage tanks configured to store a natural gas supply for fueling the at least one natural gas and/or dual fuel powered engine.

The one or more storage tanks may be located onboard the locomotive.

The hybrid power system may include at least one modular unit disposed on the locomotive, the at least one modular unit having the at least one natural gas powered engine and the one or more storage tanks for storing the natural gas.

The at least one diesel and/or dual fuel powered engine may include a plurality of diesel and/or dual fuel engines.

The at least one diesel and/or dual fuel powered engine may have a NOx emission rate of less than 2.0 g/bhp-hr, more particularly less than 1.5 g/bhp-hr, more particularly about 1.3 g/bhp-hr or less, and more particularly about 0.8 g/bhp-hr or less.

The at least one diesel and/or dual fuel powered engine may have a power output of between 500-3500 horsepower, more particularly between about 750-3000 horsepower, such as about 950 horsepower or about 2700 horsepower.

The at least one diesel powered engine may be powered only with diesel fuel.

The hybrid power system may further include one or more storage tanks configured to store a diesel fuel supply for fueling the at least one diesel and/or dual fuel powered engine.

The at least one natural gas powered engine may be different from the at least one diesel and/or dual fuel powered engine.

The at least one diesel powered engine may also be powered at least partially by natural gas; and/or the at least one natural gas powered engine may also at least partially powered by diesel.

The hybrid power system may further include: at least one dual fuel engine powered by both natural gas and diesel fuel; wherein the drive system is operatively coupled to the at least one dual fuel engine for propelling the locomotive; and the system controller is operatively coupled to the at least one dual fuel engine for controlling the power output of the dual fuel engine based upon a determination of the desired power level to propel the locomotive.

The system controller may command the at least one dual fuel engine to supply power to the drive system for supplementing the power output of the at least one natural gas powered engine and/or the at least one diesel powered engine.

The drive system may include one or more traction motors drivingly coupled to wheels for propelling the locomotive.

The at least one natural gas powered engine, the at least one diesel powered engine, and/or the at least one dual fuel engine may be operatively coupled to one or more alternators and/or one or more electrical generators configured to convert mechanical energy from the respective engines to electrical energy, thereby providing alternating current or direct current to one or more traction motors, which transmit power to wheels for propelling the locomotive.

The system controller may control the power output from the respective engines to the one or more traction motors, and controls the power output from the one or more traction motors to the wheels.

The hybrid power system may further include a battery, the battery being operatively coupled to one or more traction motors for transmitting power to the wheels.

The battery may be operatively coupled to one or more electrical generators, the electrical generators being configured to convert mechanical energy from the at least one natural gas powered engine, the at least one diesel powered engine, and/or the at least one dual fuel engine into electrical energy for charging the battery.

The system controller may be operatively coupled to battery to receive power, and the controller may be configured to charge or discharge the battery based upon the desired power demand.

The hybrid power system may further include a connection, such as an electrical bus, for being connected to an external power source, such as a power line.

The at least one natural gas powered engine, the at least one diesel powered engine, and/or the at least one dual fuel engine may be drivingly coupled to one or more wheels via a mechanical transmission.

According to another aspect of the present disclosure, a unitary locomotive having the hybrid power system according to any of the foregoing or any of the following is provided.

According to another aspect of the present disclosure, a method of operating a locomotive with a hybrid power system, includes: i) determining a desired power level for propelling the locomotive; ii) commanding at least one natural gas powered engine to supply power to a drive system up to a maximum power output of the at least one natural gas powered engine for propelling the locomotive; and iii) when the desired power level exceeds the maximum power output of the at least one natural gas powered engine, commanding at least one diesel and/or dual fuel powered engine to supply power to the drive system to supplement the power supplied by the natural gas powered engine.

According to another aspect of the present disclosure, a method of operating a locomotive according to any of the foregoing features is provided.

It is understood that embodiments of the subject matter described in this specification can be implemented in combination with digital electronic circuitry, controllers, processors, computer software, firmware, and/or hardware. For example, embodiments may be implemented in a hybrid power system for a locomotive that uses one or more modules of computer program instructions encoded on a non-transitory computer-readable medium for execution by, or to control the operation of, data processing apparatus. In the flow diagram(s), blocks may denote “processing blocks” that may be implemented with logic. The processing blocks may represent a method step or an apparatus element for performing the method step. A flow diagram does not depict syntax for any particular programming language, methodology, or style (e.g., procedural, object-oriented). Rather, a flow diagram illustrates functional information one skilled in the art may employ to develop logic to perform the illustrated processing. It will be appreciated that in some examples, program elements like temporary variables, routine loops, and so on, are not shown. It will be further appreciated that electronic and software applications may involve dynamic and flexible processes so that the illustrated blocks can be performed in other sequences that are different from those shown or that blocks may be combined or separated into multiple components. “Logic,” as used herein, includes but is not limited to hardware, firmware, software or combinations of each to perform a function(s) or an action(s), or to cause a function or action from another logic, method, or system. For example, based on a desired application or needs, logic may include a software controlled microprocessor, discrete logic like an application specific integrated circuit (ASIC), a programmed logic device, a memory device containing instructions, or the like. Logic may include one or more gates, combinations of gates, or other circuit components. Logic may also be fully embodied as software. Where multiple logical logics are described, it may be possible to incorporate the multiple logical logics into one physical logic. Similarly, where a single logical logic is described, it may be possible to distribute that single logical logic between multiple physical logics. Algorithmic descriptions and representations used herein are the means used by those skilled in the art to convey the substance of their work to others. An algorithm or method is here, and generally, conceived to be a sequence of operations that produce a result. The operations may include physical manipulations of physical quantities. Usually, though not necessarily, the physical quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated in a logic and the like. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. It should be borne in mind, however, that these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise, it is appreciated that throughout the description, terms like processing, computing, calculating, determining, displaying, or the like, refer to actions and processes of a computer system, logic, processor, or similar electronic device that manipulates and transforms data represented as physical (electronic) quantities. It will be appreciated that the processes may be implemented using various programming approaches like machine language, procedural, object oriented or artificial intelligence techniques. In one example, methodologies are implemented as processor executable instructions or operations provided on a computer-readable medium. Thus, in one example, a computer-readable medium may store processor executable instructions operable to perform a method. The computer-readable medium may be a hard-drive, a machine-readable storage device, a memory device, or a combination of one or more of them. The controller may include all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The controller may include, in addition to hardware, code that creates an execution environment for the computer program in question. The computer program (also referred to as software or code), may be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. The computer program may be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network. The processor may include all apparatus, devices, and machines suitable for the execution of a computer program, which may include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, the processor will receive instructions and data from a read-only memory or a random access memory or both. The computer may include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data. Devices suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry. To provide for interaction with a user, embodiments may be implemented using a computer having a display device and an input device. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input. Embodiments may include a computing system that includes a back-end component (e.g., as a data server), or that includes a middleware component (e.g., an application server), or that includes a front-end component (e.g., a client computer having a graphical user interface through which a user can interact with an implementation of the subject matter described is this specification), or any combination of one or more such back-end, middleware, or front-end components. The components of the system can be interconnected by any form or medium of digital data communication.

As used herein, an “operable connection,” or a connection by which entities are “operably connected,” is one in which the entities are connected in such a way that the entities may perform as intended. An operable connection may be a direct connection or an indirect connection in which an intermediate entity or entities cooperate or otherwise are part of the connection or are in between the operably connected entities. For example, an “operable connection,” or a connection by which entities are “operably connected,” is one in which signals, physical communications, or logical communications may be sent or received. Typically, an operable connection may include a physical interface, an electrical interface, or a data interface, but it is to be noted that an operable connection may include differing combinations of these or other types of connections sufficient to allow operable control. For example, two entities can be operably connected by being able to communicate signals to each other directly or through one or more intermediate entities like a processor, operating system, a logic, software, or other entity. Logical or physical communication channels can be used to create an operable connection.

As used herein, it is to be understood that terms such as “top,” “bottom,” “upper,” “lower,” “left,” “right,” “front,” “rear,” “forward,” “rearward,” and the like as used herein may refer to an arbitrary frame of reference, rather than to the ordinary gravitational frame of reference.

It is to be understood that all ranges and ratio limits disclosed in the specification and claims may be combined in any manner. It is to be understood that unless specifically stated otherwise, references to “a,” “an,” and/or “the” may include one or more than one, and that reference to an item in the singular may also include the item in the plural.

The term “about” as used herein refers to any value which lies within the range defined by a variation of up to ±10% of the stated value, for example, ±10%, ±9%, ±8%, ±7%, ±6%, ±5%, ±4%, ±3%, ±2%, ±1%, ±0.01%, or ±0.0% of the stated value, as well as values intervening such stated values. Unless otherwise stated above, in the tables of FIGS. 5A-7B, the stated values in each column and row may be “about” those stated values, which may be rounded to the nearest tenth, hundredth, thousandth, ten-thousandth, etc., and may encompass the foregoing variation of up to ±10% of those stated values, including the values intervening such variance.

The phrase “and/or” should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified unless clearly indicated to the contrary. Thus, as a non-limiting example, a reference to “A and/or B,” when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

The word “or” should be understood to have the same meaning as “and/or” as defined above. For example, when separating items in a list, “or” or “and/or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of” or “exactly one of,” may refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.”

The transitional words or phrases, such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” and the like, are to be understood to be open-ended, i.e., to mean including but not limited to.

Although the present disclosure has shown and described a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments according to the present disclosure. In addition, while a particular feature according to the present disclosure may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application. 

1. A hybrid power system for a locomotive, comprising: at least one engine powered by natural gas; at least one engine powered by diesel fuel and/or a dual fuel mixture of diesel and natural gas; a drive system operatively coupled to the at least one natural gas powered engine and the at least one diesel and/or dual fuel powered engine for propelling the locomotive; and a system controller operatively coupled to the at least one natural gas powered engine, the at least one diesel and/or dual fuel powered engine, and the drive system; wherein the system controller is configured to: i) determine a desired power level for propelling the locomotive; ii) command the at least one natural gas powered engine to supply power to the drive system up to a maximum power output of the at least one natural gas powered engine; and iii) when the desired power level exceeds the maximum power output of the at least one natural gas powered engine, command the at least one diesel and/or dual fuel powered engine to supply power to the drive system to supplement the power supplied by the natural gas powered engine.
 2. The hybrid power system according to claim 1, wherein the at least one natural gas powered engine includes a plurality of natural gas powered engines; and wherein the system controller is configured to: command one or more of the plurality of natural gas powered engines to supply power to the drive system up to a maximum cumulative power output of the one or more natural gas powered engines; and when the desired power level for propelling the locomotive exceeds the maximum cumulative power output of the one or more natural gas powered engines, command one or more additional natural gas powered engines of the plurality of natural gas powered engines to supply power to the drive system for supplementing the cumulative power output of the first-mentioned one or more natural gas powered engines.
 3. The hybrid power system according to claim 1, wherein the at least one diesel and/or dual fuel powered engine includes a plurality of diesel and/or dual fuel powered engines; and wherein the system controller is configured to: command one or more of the plurality of diesel and/or dual fuel powered engines to supply power to the drive system up to a maximum cumulative power output of the one or more diesel and/or dual fuel engines; and when the desired power level for propelling the locomotive exceeds the maximum cumulative power output of the one or more diesel and/or dual fuel powered engines, command one or more additional diesel and/or dual fuel powered engines of the plurality of diesel and/or dual fuel powered engines to supply power to the drive system for supplementing the cumulative power output of the first-mentioned one or more diesel and/or dual fuel powered engines.
 4. The hybrid power system according to claim 1, wherein the desired power level includes a plurality of discrete graduated power levels that are selectable, in which the discrete graduate power levels correspond to a notch schedule.
 5. The hybrid power system according to claim 1, wherein the at least one natural gas powered engine and the at least one diesel and/or dual fuel powered engine each have an emissions rate of one or more emissions including nitrogen oxides (NOx), particulate matter (PM), and/or hydrocarbons (NC); and wherein the controller is configured to control the power output of the at least one natural gas powered engine and the at least one diesel and/or dual fuel powered engine for minimizing the combined emissions rate to below 0.2 g/bhp-hr NOx as an average percentage of the duty cycle.
 6. The hybrid power system according to claim 1, wherein the at least one natural gas powered engine has a NOx emission rate of less than 1.0 g/bhp-hr, and wherein the at least one natural gas powered engine has a power output of between 100-500 horsepower.
 7. The hybrid power system according to claim 1, wherein the at least one natural gas powered engine is powered only with natural gas.
 8. The hybrid power system according to claim 1, wherein the at least one diesel and/or dual fuel powered engine has a NOx emission rate of less than 2.0 g/bhp-hr, and wherein the at least one diesel and/or dual fuel powered engine has a power output of between 500-3500 horsepower.
 9. The hybrid power system according to claim 1, wherein the at least one diesel powered engine is powered only with diesel fuel.
 10. The hybrid power system according to claim 1, wherein the at least one natural gas powered engine is different from the at least one diesel and/or dual fuel powered engine.
 11. The hybrid power system according to claim 1, wherein the at least one diesel powered engine is also powered at least partially by natural gas; and/or wherein the at least one natural gas powered engine is also at least partially powered by diesel.
 12. The hybrid power system according to claim 1, further comprising: at least one dual fuel engine powered by both natural gas and diesel fuel; wherein the drive system is operatively coupled to the at least one dual fuel engine for propelling the locomotive; and the system controller is operatively coupled to the at least one dual fuel engine for controlling the power output of the dual fuel engine based upon a determination of the desired power level to propel the locomotive.
 13. The hybrid power system according to claim 1, wherein the system controller commands the at least one dual fuel engine to supply power to the drive system for supplementing the power output of the at least one natural gas powered engine and/or the at least one diesel powered engine.
 14. The hybrid power system according to claim 1, wherein the at least one natural gas powered engine, the at least one diesel powered engine, and/or the at least one dual fuel engine are operatively coupled to one or more alternators and/or one or more electrical generators configured to convert mechanical energy from the respective engines to electrical energy, thereby providing alternating current or direct current to one or more traction motors, which transmit power to wheels for propelling the locomotive.
 15. The hybrid power system according to claim 1, wherein the system controller controls the power output from the respective engines to the one or more traction motors, and controls the power output from the one or more traction motors to the wheels.
 16. The hybrid power system according to claim 1, further comprising a battery, the battery being operatively coupled to one or more traction motors for transmitting power to the wheels.
 17. The hybrid power system according to claim 16, wherein the battery is operatively coupled to one or more electrical generators, the electrical generators being configured to convert mechanical energy from the at least one natural gas powered engine, the at least one diesel powered engine, and/or the at least one dual fuel engine into electrical energy for charging the battery.
 18. The hybrid power system according to claim 16, wherein the system controller is operatively coupled to battery to receive power, and the controller is configured to charge or discharge the battery based upon the desired power demand.
 19. The hybrid power system according to claim 1, further comprising a connection, such as an electrical bus, for being connected to an external power source, such as a power line.
 20. A method of operating a locomotive with a hybrid power system, the method comprising: i) determining a desired power level for propelling the locomotive; ii) commanding at least one natural gas powered engine to supply power to a drive system up to a maximum power output of the at least one natural gas powered engine for propelling the locomotive; and iii) when the desired power level exceeds the maximum power output of the at least one natural gas powered engine, commanding at least one diesel and/or dual fuel powered engine to supply power to the drive system to supplement the power supplied by the natural gas powered engine. 